Brain tumors account for 85% to 90% of all primary central nervous system (CNS) tumors (see, e.g., Levin V. A., et al., Cancer: Principles and Practice of Oncology. 6th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins, 2001, pp 2100-60; herein incorporated by reference in its entirety). Available registry data from the Surveillance, Epidemiology, and End Results (SEER) database for 1996 to 2000 indicate that the combined incidence of primary invasive CNS tumors in the United States is 6.6 per 100,000 persons per year, with an estimated mortality of 4.7 per 100,000 persons per year (see, e.g., Trends in SEER incidence and U.S. mortality using the joinpoint regression program 1975-2000 with up to three joinpoints by race and sex. In: Ries LAG, Eisner M P, Kosary CL, et al.: SEER Cancer Statistics Review, 1975-2000. Bethesda, Md.: National Cancer Institute, 2003; herein incorporated by reference in its entirety). Worldwide, approximately 176,000 new cases of brain and other CNS tumors were diagnosed in the year 2000, with an estimated mortality of 128,000 (see, e.g., Parkin D. M., et al., Int J Cancer 94 (2): 153-6, 2001; herein incorporated by reference in its entirety). In general, the incidence of primary brain tumors is higher in whites than in blacks, and mortality is higher in males than in females (see, e.g., Levin V. A., et al., Cancer: Principles and Practice of Oncology. 6th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins, 2001, pp 2100-60; herein incorporated by reference in its entirety).
Metastatic tumors are among the most common mass lesions in the brain. In recent years the incidence of CNS metastasis has increased. This is because, for example, the median survival duration of cancer patients has increased as a result of modern therapies, increased availability of advance imaging techniques, and vigilant surveillance protocols. Unfortunately, some chemotherapeutic agents can weaken the blood-brain barrier (BBB) transiently and allow CNS seeding. Moreover, a number of commonly used chemotherapeutic agents do not cross the BBB, thus leaving the brain as a safe haven for tumor growth. Metastases from systemic cancer can affect brain parenchyma, its covering, and the skull. Different tumors metastasize to different organs preferentially. Generally, cells with similar origins are believed to have similar growth constraints and to embryologically express similar sets of adhesive molecules such as addressins. In the United States, incidence of metastatic brain tumor is exceeding that of primary brain tumor. Metastatic brain tumors comprise 50% of all brain tumors and as many as 30% of tumors diagnosed by imaging study alone. The incidence is estimated to be 100,000 new cases per year in the United States. In autopsy studies, over 20% patients with systemic neoplastic disease have brain metastasis.
The clinical presentation of various brain tumors is best appreciated by considering the relation of signs and symptoms to anatomy (see, e.g., Levin V. A., et al., Cancer: Principles and Practice of Oncology. 6th ed. Philadelphia, Pa.: Lippincott Williams & Wilkins, 2001, pp 2100-60; herein incorporated by reference in its entirety). General signs and symptoms include headache, gastrointestinal symptoms (e.g., nausea, loss of appetite, and vomiting) and changes in personality (e.g., changes in mood, mental capacity, and concentration). Whether primary, metastatic, malignant, or benign, brain tumors must be differentiated from other space-occupying lesions such as abscesses, arteriovenous malformations, and infarction, which can have a similar clinical presentation (see, e.g., Hutter A, et al., Neuroimaging Clin N Am 13 (2): 237-50, x-xi, 2003; herein incorporated by reference in its entirety).
Surgery is the treatment of choice for accessible brain tumors. Accessible tumors are those that can be surgically removed without causing severe neurological damage. Deeply seated tumors (e.g., brain tumors located in the brain stem, the thalamus, the motor area, and the deep areas of gray matter) may be inaccessible, and as such, inoperable. The goal of surgery is to remove all or most of the visible tumor. Many benign tumors are treated only by surgery. Most malignant tumors require additional treatment. Malignant tumors lack distinct borders. They often invade nearby normal brain tissue. Tumor cells may also spread throughout the brain and spine by way of the cerebrospinal fluid. But, even partial tumor removal is beneficial.
There are several purposes of brain tumor related neurosurgery. One purpose of brain tumor related surgery is to remove as much tumor as possible. Partial brain tumor removal (e.g., debulking) provides relief of symptoms, improved quality of life, and a smaller tumor burden for other treatment modalities. Brain tumor related neurosurgery also assists in establishing an exact diagnosis. For example, removal of a sample of tumor (e.g., a tumor biopsy) to be examined under a microscope in the laboratory provides an exact diagnosis. Furthermore, brain tumor related neurosurgery provides access for other treatments. For example, during neurosurgery radiation implants or chemotherapy-impregnated wafers may be delivered to the brain tumor. Biopsy alone is performed when the tumor is inoperable or when surgery must be delayed. Resection (e.g., surgical removal of a tumor) is the treatment of choice whenever possible.
Neurosurgery, however, demands special considerations. Obtaining surgical access to brain tumors requires the creation of an opening in the skull (called a craniotomy). Most often, a craniotomy involves a large incision and dissection of other soft tissue that results in significant postoperative pain and discomfort. Furthermore, reaching deep tumors in the brain requires openings into the surface of the brain itself. This brain dissection and manipulation can result in neurological deficits.
What is needed are improved neurosurgical techniques for accessing brain locations. Additionally, what are needed are improved devices assisting in neurosurgical techniques that limit soft tissue dissection and potential brain manipulation and damage. Additionally, what is needed are improved devices for cutting, cauterizing and aspirating brain tumors through small openings in the skull and brain tissue.